1. Field of the Invention
The present invention relates to surgical theaters, surgical procedures and apparatus for performing surgical procedures which combine magnetic resonance imaging and magnetic stereotaxis guidance or movement of medical devices or materials. The invention also relates to the design, construction and use of a neurosurgical theater where a magnetic surgery system (MSS) is functionally integrated with a magnetic resonance imaging (MRI) system so that MRI-guided, MSS-directed diagnostic and/or therapeutic procedures may be performed within the theater.
2. Field of the Invention
The concept of administering minimally invasive therapy, including minimally invasive drug delivered therapy follows recent trends in medical and surgical practice towards increasing simplicity, safety, and therapeutic effectiveness. Image-guided, minimally invasive therapies have already superseded conventional surgical methods in several procedures. For example, transvascular coronary angioplasty is often now an alternative to open-heart surgery for coronary artery bypass, and laparascopic cholecystectomy is often an alternative to major abdominal surgery for gall bladder removal. The use of the less invasive techniques has typically reduced hospital stays by 1-2 weeks and the convalescence periods from 1-2 months to 1-2 weeks.
While endoscopic, arthroscopic, and endovascular therapies have already produced significant advances in health care, these techniques ultimately suffer from the same limitation. This limitation is that the accuracy of the procedure is "surface limited" by what the surgeon can either see through the device itself or otherwise visualize (as by optical fibers) during the course of the procedure. That is, the visually observable field of operation is quite small and limited to those surfaces (especially external surfaces of biological masses such as organs and other tissue) observable by visible radiation, due to the optical limitations of the viewing mechanism. MR imaging, by comparison, overcomes this limitation by enabling the physician or surgeon to non-invasively visualize tissue planes and structures (either in these planes or passing through them) beyond the surface of the tissue under direct evaluation. Moreover, MR imaging enables differentiation of normal from abnormal tissues, and it can display critical structures such as blood vessels in three dimensions. Prototype high-speed MR imagers which permit continuous real-time visualization of tissues during surgical and endovascular procedures have already been developed. MR-guided minimally invasive therapy is expected to substantially lower patient morbidity because of reduced post-procedure complications and pain. The use of this type of procedure will translate into shorter hospital stays, a reduced convalescence period before return to normal activities, and a generally higher quality of life for patients. The medical benefits and health care cost savings are likely to be very substantial.
A specific area where research is moving forward on advances of this type is in the treatment of neurological disorders. Specifically, the advent of new diagnostic and therapeutic technologies promises to extend the range of application and the utility of intracerebral drug delivery procedures and thus possibly advance the efficacy of existing and/or planned treatments for various focal neurological disorders, neurovascular diseases and neurodegenerative processes. Currently, when the standard procedure requires neurosurgeons or interventional neuroradiologists to deliver drug therapy into the brain, the drug delivery device, such as a catheter, must either be passed directly through the intraparenchymal tissues to the targeted region of the brain, or guided through the vasculature until positioned properly. An important issue in either approach is the accuracy of the navigational process used to direct the movement of the drug delivery device. In many cases, the physical positioning of either part or all of the catheter's lumen within the brain is also important as, for example, in situations where a drug or some other therapeutic agent will be either infused or retroperfused into the brain through the wall or from the tip of the catheter or other drug delivery device.
New technologies like intra-operative magnetic resonance imaging and nonlinear magnetic stereotaxis, the latter discussed by G. T. Gillies, R. C. Ritter, W. C. Broaddus, M. S. Grady, M. A. Howard III, and R. G. McNeil, "Magnetic Manipulation Instrumentation for Medical Physics Research," Review of Scientific Instruments, Vol.65, No.3, pp.533-562 (March 1994), as two examples, will likely play increasingly important roles here. In the former case, one type of MR unit is arranged in a "double-donut" configuration, in which the imaging coil is split axially into two components. Imaging studies of the patient are performed with this system while the surgeon is present in the axial gap and carrying out procedures on the patient. A second type of high-speed MR imaging system combines high-resolution MR imaging with conventional X-ray fluoroscopy and digital subtraction angiography (DSA) capability in a single hybrid unit. These new generations of MR scanners are able to provide the clinician with frequently updated images of the anatomical structures of interest, therefore making it possible to tailor a given interventional procedure to sudden or acute changes in either the anatomical or physiological properties of, e.g., a part of the brain into which a drug agent is being infused.
Nonlinear magnetic stereotaxis is the image-based magnetically guided movement of a catheter or some other form of a (temporary or lermanent) implant directly through the bulk brain tissues or along tracts within the neurovasculature or elsewhere within the body. Electromagnets or permanent magnets are used to magnetically steer the implant, giving (for example) the neurosurgeon or interventional neuroradiologist the ability to guide the object along a particular path of interest. (The implant might be either magnetically and/or mechanically advanced towards its target, but is magnetically steered, in either case. That is, magnetic fields and gradients are used to provide torques and forces (including linear forces) to orient or shift the position of the implant or device, with a mechanical pushing force subsequently providing none, some, or all of the force that actually propels the implant or device. Additional force may be provided magnetically, hydraulically or by some other force means.) The implant's position is monitored by biplanar fluoroscopyor some other non-invasive visualization or imaging method, and its location is or can be indicated on a computerized atlas of brain images derived from a pre-operative MR scan. Among other applications, the implant might be used to tow a pliable catheter or other drug delivery device to a selected intracranial location through the brain parenchyma or via the neurovasculature. Magnetic manipulation of catheters and other probes is well documented in research literature. For example, Cares et al. (J. Neurosurg, 38:145, 1973) have described a magnetically guided microballoon released by RF induction heating, which was used to occlude experimental intracranial aneurysms. More recently, Kusunoki et al. (Neuroradiol 24: 127, 1982) described a magnetically controlled catheter with cranial balloon useful in treating experimental canine aneurysms. Ram and Meyer (Cathet. Cardiovas. Diag.22:317, 1991) have described a permanent magnet-tipped polyurethane angiography catheter useful in cardiac interventions, in particular intraventricular catheterization in neonates.
U.S. Pat. No. 4,869,247 teaches the general method of intraparenchymal and other types of magnetic manipulation, and U.S. Pat. Nos. 5,125,888; 5,707,335; and 5,779,694 describe the use of nonlinear magnetic stereotaxis to maneuver a drug or other therapy delivery catheter system within the brain. U.S. Pat. No. 5,654,864 teaches a general method of controlling the operation of the multiple coils of a magnetic stereotaxis system for the purpose of maneuvering an implant to precisely specified locations within the body.
Both of these technologies offer a capability for performing image-guided placement of a catheter or other drug delivery device, thus allowing drug delivery directly into selected brain tissues via infusion through the walls of the catheter or outflow from the tip of the catheter. In the case of drug delivery directly into the brain tissues, the screening of large molecular weight substances by the endothelial blood-brain barrier can be overcome. In the case of infusions into specific parts of the cerebrovasculature, highly selective catheterizations can be enabled by these techniques. In either case, however, detailed visual images denoting the actual position of the drug delivery device within the brain would be extremely useful to the clinician in maximizing the safety and efficacy of the procedure. The availability of an MR-visible drug delivery device combined with MR-visible drug agents would make it possible to obtain near real-time information on drug delivery during interventional procedures guided by non-linear magnetic stereotaxis. Drug delivery devices, such as catheters, that are both MR-visible and radio-opaque could be monitored by at least two modalities of imaging, thus making intra-operative verification of catheter location possible during nonlinear magnetic stereotaxis procedures. (Intra-operative MR assessment might require the temporary removal of the magnetic tip and/or any other magnetic or magnetic responsive component or element of the drug delivery catheter and interruption of the magnetic stereotaxis procedure to image the patient.).
The geometry and magnetic strength of the magnetic tip will depend upon the particular type of catheter or medical device with which the tip is being used. In a preferred embodiment, the tip would have as small a maximum dimension as would be consistent with maintaining sufficient magnetic dipole moment to couple satisfactorily to the external magnetic fields and gradients used to apply torques and forces to the tip for the purpose of steering or moving the catheter or other medical device. Typical sizes of the tip have ranged from a few tenths of a millimeter to several millimeters in maximum dimension in the various exploratory versions of such devices that have been studied to date. To that end, the tip might be made of a permanently magnetic or magnetically permeable material, with compounds of Nd--B--Fe being exemplary, as well as various iron alloys (ferrites and steel alloys). The magnetic tip may be fixed to the distal end of the catheter in any number of ways, depending in part upon the method of use of the catheter, the specific type of catheter, the procedures and the use of the catheter. In one design, the magnetic tip might simply be a small spherical or oblate spheroid of magnetic material (e.g., having a geometry where the semi-major axis is from 1.1 to 3 times longer, preferably from 1.5 to 2.0 or 2.5 times longer than the semi-minor axis). The magnetic tip may be originally fixed to the distal end of the catheter or medical device or passed through the length of the catheter so that it abuts against the internal distal end of the catheter (as a foot would abut the end of a sock). As noted, the magnetic tip may be fixed in place either on the inside, outside or embedded within the composition of the distal end of the catheter or medical device. In a preferred embodiment, the magnetic tip may be thermally, solubly, mechanically, electronically or otherwise removably attached to and separable from the distal end of the catheter or medical device. For instance, a heat soluble link is taught in U.S. Pat. No. 5,125,888.
In still another embodiment, the magnetic tip would constitute a plug in the end of an otherwise open-ended catheter, and the tip might either have an open bore along its axis, a plurality of open bores along its axis, or a single or plural configuration of holes along the side of the magnetic tip, any of which openings would be used to facilitate drug delivery from the catheter or to serve as an exit port for the delivery of some other therapy or device into a body part, such as the parenchymal tissues and/or the cerebrovasculature of the brain. Alternatively, the magnetic tip might simply constitute a solid plug that seals the end of the catheter. The distal end of the catheter at which the magnetic tip is placed must be configured such that axial forces and torques applied by either magnetic fields and gradients or by a guide wire internal to the catheter allow said distal end and magnetic tip to be propelled towards a target site within the body, and to do so without said distal end and magnetic tip separating from each other in an inappropriate way and/or at an undesired time or under undesired circumstances. If the magnetic tip must be removed, or detached and removed, for example, prior to MR imaging of the patient, such a procedure could be accomplished by the method taught in U.S. Pat. No. 5,125,888; 5,707,335; and 5,779,694, which call for dissolving a heat separable link between the tip and the catheter by a pulse of radio-frequency energy. An alternative means of removing the magnetic tip is discussed by M. A. Howard et al. in their article, "Magnetically Guided Stereotaxis," in Advanced Neurosurgical Navigation, edited by E. Alexander III and R. J. Maciunas (Thieme Medical Publisher, New York, 1998), which calls for withdrawing the magnetic tip from along the inside of the catheter that it has just steered into place within the body. Without removal of the magnetic tip from the catheter, whole body magnetic forces might be produced on it by the field of the MR imaging system, and these could cause undesired movement of the catheter within the body.
In the treatment of neurological diseases and disorders, targeted drug delivery can significantly improve therapeutic efficacy, while minimizing systemic side-effects of the drug therapy. Image-guided placement of the tip of a drug delivery catheter directly into specific regions of the brain can initially produce maximal drug concentration close to some targeted loci of tissue receptors following delivery of the drug. At the same time, the limited distribution of drug injected from a single catheter tip presents other problems. For example, the volume flow rate of drug delivery must be very low to avoid indiscriminate hydrodynamic damage or other damage to brain cells and nerve fibers. Delivery of a drug from a single point source may also limit the distribution of the drug by decreasing the effective radius of penetration of the drug agent into the surrounding tissue receptor population. Positive pressure infusion, i.e., convection-enhanced delivery of drugs into the brain, as taught by U.S. Pat. No. 5,720,720 may overcome the problem of effective radius of penetration. Also, U.S. patent application Ser. No. 08/857,043, filed on May 15, 1997 and titled "Method and Apparatus for Use with MR Imaging" describes a technology invented in-part by one of the present inventors comprising a method for observing the delivery of material to tissue in a living patient comprising the steps of a) observing by magnetic resonance imaging a visible image within an area or volume comprising tissue of said living patient, the area or volume including a material delivery device, b) delivering at least some material by the material delivery device into the area or volume comprising tissue of a living patient, and c) observing a change in property of said visible image of the area or volume comprising tissue of a living patient while said material delivery device is still present within the area or volume. This process, including the MRI visualization, is performed in approximately or actually real time, with the clinical procedure being guided by the MRI visualization.
Research on magnetic catheterization of cerebral blood vessels generally has focused on design of transvascular devices to thrombose aneurysms, to deliver cytotoxic drugs to tumors, and to deliver other therapies without the risks of major invasive surgery. Examples of such studies include Hilal et al (J. Appl. Phys. 40:1046, 1969), Molcho et al (IEEE Trans. Biomed. Eng. BME-17, 134, 1970), Penn et al (J. Neurosurg. 38:239, 1973), and Hilal et al (Radiology 113:529,1974). U.S. Pat. Nos. 4,869,247, 5,654,864, 5,125,888, 5,707,335 and 5,779,694 describe processes and apparatus for the use of magnetic stereotaxis for the manipulation of an object or implant which is moved into position within a patient, particularly within the cranial region and specifically within the brain but in principle elsewhere in the body also. These patents do no not involve any contemplation of real time visualization of drug distribution within the brain, especially by MRI. It should be noted that the potential exists for interactive interference between the two systems, magnetic resonance imaging and magnetic stereotaxis, particularly where fine images are being provided by a system based on magnetic microcoils, especially as described in U.S. patent application Ser. No. 08/916,596, filed on Aug. 22, 1997, which is incorporated herein by reference for its disclosure of the design, construction, structure and operation of such coils and such catheters in MR-guided procedures.
A source of drug delivery can be effected by devising a multi-lumen catheter with multiple drug release sources that effectively disperse therapeutic drug agents over a brain region containing receptors for the drug, or over an anatomically extensive area of brain pathology. A preferred type of structure is described in U.S. patent application Ser. No. 08/916,596, filed on Aug. 22, 1997, but other devices which are described in the background of the art in that application could also be used in the practice of the present invention.
The present invention describes methods for exploiting interactive interference between magnetic resonance imaging systems and magnetic stereotaxis systems. Both modalities rely on the creation of large external magnetic fields to function as designed. The magnetic field and field gradients of the magnetic stereotaxis system are used to steer an implant within the body, and especially within the brain, while the magnetic fields of the magnetic resonance imager are used to create images of the planes of tissue within the patient's body. The magnetic fields of either one of these systems/devices can perturb the size and shape (and, therefore, the function) of the fields of the other device. It is unlikely that a clinical configuration of these systems/devices would be purposely arranged so as to cause direct interference via interaction of the fields. However, a far more likely danger is that the magnetic tip of the implanted catheter or other MSS-guided device will experience bulk-body forces and torques if the patient is placed in the MR and is subjected to the resulting magnetic field produced during the course of its functioning. Such a field could very easily cause the magnetically-tipped implant to move away from the location into which it was navigated by the clinician operating the magnetic stereotaxis system. This might produce a dangerous situation for the patient and, hence, care must be taken to insure that the magnetic tip is either removed from the catheter in the patient prior to MR imaging, or that it is otherwise deactivated or made impervious to the effects of non-MSS fields to which it might be subjected. Moreover, the presence of a relatively large magnetic dipole in the patient's body, as might arise from the presence of the magnetic tip of the implanted catheter, would create artifacts in the MR images.
Neurosurgical procedures require precise anatomic localization of normal and abnormal tissues. Present systems of image-guided neurosurgery include framed and frameless technologies, which typically use images acquired preoperatively to create a three-dimensional space on which the surgical navigation is based. Framed systems use externally applied frames to establish the fiducials for navigation, whereas frameless systems use optical, electromagnetic, or ultrasound sensors and/or mechanical anus to identify anatomical locations and/or to track the position of surgical tools and instruments during surgical procedures. Some systems of frameless stereotaxis also attempt to use natural anatomical features of the head as reference points in the navigation process.
A variety of framed and frameless imaging and therapy delivery systems have been described in the art, representative examples of which are as follows:
U.S. Pat. No. 4,791,934 to Brunnett discloses a system in which a CT scan is acquired at one location, and is digitally stored in a computer. At a second location, the patient undergoes X-ray imaging, which is also stored in a computer. The X-ray image is then registered with the CT image in 3 dimensions to enable a surgeon to plan a best trajectory for a biopsy needle. U.S. Pat. No. 5,078,140 to Kwoh discloses an imaging device-aided robotic stereotaxis system, wherein an imaging system provides information about a body structure to a computer which controls a robotic arm which orients the surgical devices. U.S. Pat. No. 5,242,455 to Skeens and Miketic and U.S. Pat. No. 5,305,203 to Raab disclose methods for stereotactic placement of probes into a body region utilizing an imaging system, wherein the mechanical control system for placing the probe is imaged within the reference images of the body. U.S. Pat. Nos. 5,339,812 and 5,553,112 to Hardy et al. disclose(s) an image-based model for the planning and delivery of therapy to the body, wherein MRI or CT imaging data are used to provide three-dimensional stereotactic coordinates to guide anatomically targeted therapy. U.S. Pat. No. 5,309,923 to Kormos et al. and U.S. Pat. No. 5,517,990 to Kalfas et al. disclose a stereotaxy wand and tool guide, wherein a trajectory and location of the wand are superimposed on a diagnostic image on a monitor.
U.S. Pat. No. 5,230,338 to Allen et al. discloses an interactive image-guided system for displaying images corresponding to the placement of a surgical probe in the body. U.S. Pat. No. 4,173,228 to Van Steenwyk et al., and U.S. Pat. No. 5,042,486 to Pfeiler et al. disclose medical probes wherein electromagnetic signals are propagated between one antenna on the tip of the probe inserted into a body region and several antennae outside the body. The position and orientation of the probe tip are determined from the signals transmitted between said antennae. U.S. Pat. No. 5,211,165 to Dumoulin et al., U.S. Pat. No. 5,255,680 to Darrow and Dumoulin, U.S. Pat. No. 5,307,808 to Dumoulin et al., and U.S. Pat. No. 5,318,025 to Dumoulin et al. additionally disclose a tracking system in which radiofrequency signals emitted by an invasive device, such as a catheter, are detected and used to measure the device's position and orientation in a patient. Localization of devices in situ is achieved by transmitter radiofrequency coils positioned at its distal end, which are detected by receiver radiofrequency coils positioned around the imaging volume of interest. The position of the device, as determined by the tracking system, is superimposed upon independently acquired diagnostic images. U.S. Pat. No. 5,383,454 to Bucholz discloses a system for indicating a position of a tip of a probe which is positioned within an object on images of the object, wherein a computer employing translational software translates the position of the tip of said probe into a coordinate system corresponding to the coordinate system of the cross-sectional images.
U.S. Pat. No. 5,279,309 to Taylor et al. and U.S. Pat. No. 5,445,166 to Taylor disclose a system for positioning an object at a target location in a body, wherein a computer determines a surgical plan. U.S. Pat. No. 5,558,091 to Acker et al. discloses a system utilizing magnetic fields, wherein the position and orientation of probes within the magnetic fields can be determined within a body. U.S. Pat. No. 5,218,964 to Sepponen discloses a method for providing reference markers in MR images, wherein during MR imaging of a region of the body electron spin resonance energy is supplied to the reference markers to amplify the MR signal by dynamic nuclear polarization. U.S. Pat. No. 5,474,565 to Clayman and Nguyen discloses a method of performing a neurological procedure on a human, wherein an image is obtained of the patient's head, the patient is moved to the operating room, and the imaging data is used in conjunction with the cerebral instrument guide frame to guide one or more medical instruments.
U.S. Pat. No. 5,590,653 to Aida et al. discloses an ultrasonic wave medical treatment apparatus which can be used under MR imaging guidance. In this invention the ultrasonic wave applicator is incorporated into a surface coil for taking MR images. U.S. Pat. No. 5,483,961 to Kelly and Goerss discloses a magnetic field digitizer for stereotactic surgery. U.S. Pat. No. 5,654,864 to Ritter et al. discloses a control method for a magnetic stereotaxis system whereby a computer can control the operation of multiple superconducting magnetic coils to guide a magnetic object based on stored preoperative images and interoperative fluoroscopic images. U.S. Pat. No. 5,705,335 to Howard et al. discloses an MSS treatment delivery apparatus comprising a magnetic object and a treatment carrier device which is connected by a heat-sensitive biodegradable connector link to the magnetic object. In the method of this invention, a robotically moved electromagnet or multicoil electromagnet system moves the magnetic object within the body to a target location determined by a clinician-operated computer.
U.S. Pat. No. 5,713,357 to Meulenbrugge et al. discloses an MR imaging system in close physical proximity to an X-ray device, to enable the patient to more easily undergo both MR imaging and X-ray imaging. A method of minimizing incompatibility between the MR imager and the X-ray device is provided by using a solid-state X-ray detector which includes a solid-state image pick-up device, and by making the position of the X-ray tube dependent on the static magnetic field of the MR scanner. When interventional techniques are commonly applied in combination with a magnetic resonance imaging device, the organs are suitably visualized, but the instruments were not sufficiently visible. The patent suggests a solution of arranging the X-ray device immediately adjacent to or in the MR device so that the patient does not have to be transported. This latter arrangement in particular is contradictory to considerations of necessity if an attempt were made to use both MR imaging and linear magnetic stereotaxis, where the operation of the two systems within the identical environment at the same time would be completely incompatible.
Framed and frameless systems have thus produced significant advances in neurosurgery. The frameless systems in particular allow the surgeon to apply a probe to the surface of the brain, and then view on a computer monitor the preoperatively imaged, subsurface planes of tissue orthogonal to the axial direction of the probe. This information may have great value to the surgeon, since the display of images correlated to a specific point or region within the brain where the neurosurgeon is working provides a distinct advantage over the simple fixed display of an atlas of the three orthogonal sets of slices as might be shown on a light box on the wall of the operating room.
Recent applications of both framed and frameless stereotaxy systems to surgery have begun to use images that are acquired in real time or close to real time. Exemplary of such applications is U.S. Pat. No. 5,531,520 to Grimson et al., which discloses an image data registration system, wherein a video camera obtains real-time images of patient anatomy which are combined with MR or CT images to provide for enhanced visualization of the anatomic region. U.S. Pat. No. 5,740,802 to Nafis et al. discloses an interactive surgery planning and display system comprising live video of external surfaces of the patient mixed with interactive computer-generated models of internal anatomy obtained from diagnostic imaging of the patient. The computer images and the live video are coordinated and displayed to a surgeon in real time in order to guide surgery. U.S. Pat. No. 5,531,227 to Schneider discloses a method and apparatus for obtaining and displaying in real time an image obtained by one modality such that the image corresponds to a line of view established by another modality. U.S. Pat. No. 5,638,819 to Manwaring and Manwaring discloses a navigational method and apparatus for guiding a surgical instrument to a target location in a body along a specified trajectory in real time.
The prior art generally describes technologies related to matching the coordinates of one imaging system with those of another imaging system. While each invention represents an advancement in the art, they fail to provide for the integrated utilization of MRI and MSS in the same room so as to guide, position, and thereafter monitor in real time the performance of MR-compatible therapeutic devices and instruments within the body without moving the patient from a single gantry. None of the patents or medical and/or scientific journal articles referenced above disclose or suggest the conjoint use of MSS/MRI to effect real-time MR image-guided visualization of MSS-directed surgical or endovascular procedures. The types of combined modality systems which have been discussed previously include ultrasonic wave applicators integrally incorporated with MRI, as in, for instance, U.S. Pat. No. 5,590,653, and live video imaging of a patient mixed and coordinated with medical diagnostic imaging data, as in U.S. Pat. No. 5,740,802. The present invention instead discloses a magnetic neurosurgery apparatus, whereby MSS and MRI are employed conjointly and interactively. U.S. Pat. No. 5,590,653 teaches that the same gantry that transports the patient into the imaging volume of the MR imager can also transport the apparatus for the delivery of an ultrasonic treatment. U.S. Pat. No. 5,255,680 teaches a means of controlling the position of the gantry transporting the patient via signals of microcoils on a medical device positioned within the patient. The present invention discloses a completely different concept, in that the same sliding gantry is used to transport the patient between functionally integrated MSS and MRI systems housed in the same room.
The use of MRI to provide intraoperative imaging guidance is a relatively new concept made feasible by the development of new MRI systems that provide high spatial and temporal resolution imaging in conjunction with multiplanar and volumetric three-dimensional data acquisition, thereby making possible interactive image plane definition to facilitate surgical localization and targeting of, for example, a lesion and improving intraoperative navigation. Intraoperative MR imaging enables the surgeon to non-invasively visualize tissue planes beyond the surface of the tissue under direct visual evaluation during a clinical procedure. Moreover, MR imaging enables differentiation of normal from abnormal tissues, and it can display critical structures such as blood vessels in three dimensions. Thus, high-speed MR-guided therapy offers an improved opportunity to maximize the benefits of minimally invasive procedures in real time.
MR imagers which permit continuous real-time visualization of tissues during surgical and endovascular procedures have already been developed. One type of MR unit designed for image-guided therapy is arranged in a "double-donut" configuration, in which the imaging coil is split axially into two components. U.S. Pat. Nos. 5,410,287, 5,519,372 and 5,565,831 provide illustrative examples of such systems. Imaging studies are performed with this system with the surgeon standing in the axial gap of the magnet and carrying out procedures on the patient. A recent article in the medical literature (P. Black et al., "Development and implementation of intraoperative magnetic resonance imaging and its neurosurgical applications," Neurosurgery, 41:831-842 (1997)) suggests that MR-guided minimally invasive therapy is expected to significantly lower patient morbidity because of reduced post-procedure complications. A second type of high-speed MR imaging system combines high-resolution MR imaging with conventional X-ray fluoroscopy and digital subtraction angiography (DSA) capability in a single hybrid unit. U.S. Pat. No. 5,713,357 to Meulenbrugge et al. describes a version of such a system. Both of these new generations of MR scanners provide frequently updated images of the anatomical structures of interest. This close to real time imaging capability makes it possible to use high-speed MR imaging to observe the effects of specific interventional procedures, such as endovascular catheter tracking and intracranial administration of drug agents to targeted tissues, as disclosed by U.S. patent application Ser. No. 08/857,043.
With MSS, the implant might be used to tow or guide a pliable catheter or other drug delivery device to a targeted intracranial location through the brain parenchyma or via the neurovasculature. U.S. Pat. No. 4,869,247 teaches the method of intraparenchymal magnetic manipulation. U.S. Pat. No. 5,654,864 teaches a method for synthesizing a control algorithm for using an MSS to deliver therapies into the body and the brain in particular, and U.S. Pat. Nos. 5,125,888; 5,707,335; and 5,779,694 disclose the use of nonlinear MSS to maneuver a catheter system within the brain.
With currently used endovascular catheterization techniques, there is generally a compromise between longitudinal and torsional rigidity for advancing and negotiating progressively more tortuous and narrow vascular lumens. As a result of these limitations associations with transarterial and transvenous manual catheterization, there has been growing interest in using magnetic fields to guide catheters through the cerebral vasculature. High-resolution visual images denoting the actual position of the medical device within the brain would be extremely useful to the clinician in maximizing the safety and efficacy of the procedure. The availability of an MR-visible drug delivery device combined with MR-visible drug agents would make it possible to obtain near real-time information on drug delivery during interventional procedures in an intraoperative MR system, as well as for postoperative confirmation of the location of the drug delivery device following a nonlinear magnetic stereotaxis procedure. Drug delivery devices, such as catheters, that are both MR-visible and radiopaque could be monitored by both X-ray fluoroscopy and MR imaging, thus making intraoperative verification of catheter location possible during nonlinear magnetic stereotaxis procedures. U.S. patent application Ser. No. 08/857,043 describes a technology comprising a method for MRI image-guided drug delivery. Active MR visualization of catheters and other interventional probes is achieved by means of radiofrequency microcoils positioned at specific points along the distal axis of the device. Another patent application co-authored by the present co-inventors and others further explores this and related approaches (U.S. patent application Ser. No. 09/131,031. Alternative means of using MR signals to localize and track devices with small coils that are placed within the body are taught by U.S. Pat. Nos. 5,211,165, 5,307,808, 5,318,025 and 5,715,822.
Both MRI and MSS enable image-guided placement of a catheter or medical device at targeted intracranial loci. An important issue in image-guided therapy is the accuracy of the navigational process used to direct the movement of the interventional medical device. The use of light-emitting diode-based optical tracking of rigid surgical instruments in combination with the manipulation of the MRI planes can provide continuous interactive feedback between the surgical maneuvers during a procedure and the corresponding images. When using flexible medical devices, such as catheters and guidewires, miniature coils attached at the distal end enable these devices to be detected deep within tissues, as disclosed by U.S. patent application Ser. No. 08/857,043. With MR coil-based tracking methods, the acquisition and display of the corresponding images can result in either the superimposition of the tips of the instruments on previously acquired images, or real-time images can be taken to establish the position of a particular device.
U.S. patent application Ser. No. 09/131,031, filed on Aug. 7, 1998 describes a method and object for selective intraparenchymal and/or neuroendovascular drug delivery and other concurrent medical treatment of abnormalities of the human central nervous system using nonlinear magnetic stereotaxis combined with magnetic resonance (MR) imaging and/or x-ray guidance.
The present invention describes specific apparatus and procedures for performing processes and apparatus in which medical treatments may be performed within a single theater where magnetic resonance imaging and magnetic stereotaxis are to be used.